Dielectric ceramic composition for microwave use

ABSTRACT

A dielectric ceramic composition for microwave use having a relative permittivity εr of 35 to 45, Qf 0  value of more than 50,000 GHz (at 7 GHz), and dielectric characteristic of τf=0±10 ppm/° C includes an La 2 O 3 .Al 2 O 3 .SrO.TiO 2  based ceramic composition and a specific quantity of Ga 2 O 3  to increase the Qf 0  value and a specific amount of Pr 2 O 3 to control the τf value.

TECHNICAL FIELD

The present invention relates to a dielectric ceramic composition for microwave use having a relative permittivity εr of 35 to 45, Qf₀ value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of τf=0±10 ppm/° C. employed for microwave communication filters, milliwave communication filters, oscillators, inductor antennas, and frequency adjusting rods etc.

BACKGROUND ART

Dielectric ceramic compositions are widely employed in the high-frequency region such as microwaves and milliwaves in for example dielectric resonators, dielectric substrates for MIC and waveguides. The characteristics that these are required to have are: (1) a large relative permittivity εr to meet demands for miniaturization, since the wavelength is reduced to 1/εr^(1/2) in a dielectric, (2) low dielectric loss at high frequency i.e. high Q value, and (3) small and stable temperature coefficient τf of resonance frequency.

Conventional examples of such a dielectric ceramic composition are La—Ti—Al—O based compositions (see Japan, J. Appl. Phys. 36 (1997) 6814), which have εr=36, Qf₀ value=45,000 GHz, and τf=−2 ppm/° C., but their Qf₀ values are low.

Also, in the case of Ba(Zn_(1/3)Nb_(2/3))O₃ based compositions (published in: Electronics/Ceramics September 1993 September page 3), εr=41, Qf₀ value=86,000 GHz, and τf=+31 ppm/° C., but a dielectric ceramic composition of small τf is not obtained.

Recently, La₂O₃.Al₂O₃.SrO.TiO₂ based composition or La₂O₃.Al₂O₃.SrO.TiO₂.CaO based composition or composition containing one or two or more of Ce, Nb, Ta, Y, Zr, V, Cr, Mo, W, Co, Ni, Cu, Zn, Sn, Bi, B, or Si in the aforementioned ceramic compositions (see Laid-open Japanese Patent Publication H. 11-130528) has been proposed.

Regarding the dielectric characteristic of these ceramic compositions, they have excellent dielectric characteristics with εr of more than 30, Qf₀ value more than 25,000 GHz (at 1 GHz) and τf less than +30 (ppm/° C.), but dielectric ceramic compositions of low τf are not obtained. Recently, with increasingly severe demands for miniaturization of portable terminal electronic equipment, materials of even better dielectric performance are being demanded.

DISCLOSURE OF THE INVENTION

In view of the foregoing demands, an object of the present invention is to provide a dielectric ceramic composition for microwave use having a relative permittivity εr of 35 to 45, Qf₀ value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of τf=0±10 ppm/° C.

The present invention studied various compositions with the object of obtaining a material capable of being controlled to a relative permittivity εr of 35 to 45, Qf₀ value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of τf=0±10 ppm/° C, and, as a result, discovered that, with an La₂O₃.Al₂O₃.SrO.TiO₂ based ceramic composition, by adding a specific quantity of Ga₂O₃ to the aforesaid ceramic composition, the Qf₀ value could be increased, and, by further adding a specific quantity of Pr₂O₃, control of the τf value became possible, so that a ceramic composition capable of being controlled to a relative permittivity εr of 35 to 45, Qf₀ value of at least 50,000 GHz (at 7 GHz) and a dielectric characteristic of τf=0±10 ppm/° C could be obtained, and thereby perfected the present invention.

Specifically, the present invention consists in a dielectric ceramic composition for microwave use characterized in that the compositional formula is expressed by aAl₂O₃.bGa₂O₃.cTiO₂.dSrO.eLa₂O₃.fPr₂O₃, where a, b, c, d, e and f representing the mol ratios satisfy the following values (the case where b and f are simultaneously 0 is excluded).

a+b+c+d+e+f=1

0.079≦a≦0.167

0≦b≦0.017

0.333≦c≦0.412

0.333≦d≦0.412

0.035≦e≦0.167

0≦f≦0.101

BEST MODE FOR CARRYING OUT THE INVENTION

The reasons why, in the present invention, if the respective mol ratios of Al₂O₃, Ga₂O₃, TiO₂, SrO, La₂O₃ and Pr₂O₃ are a, b, c, d, e, f, these mol ratios are respectively restricted to 0.079≦a≦0.167, 0≦b≦0.017, 0.333≦c≦0.412, 0.333≦d≦0.412, 0.035≦e≦0.167, and 0≦f≦0.101 are as follows.

If a is less than 0.079, εr increases but the Qf₀ value is less than 50,000 GHz, but if it exceeds 0.167 mol ratio, εr is lowered and drops to 35 or lower, which is undesirable.

If b exceeds 0.017 mol ratio, the Qf₀ value is lowered, resulting in the Qf₀ value dropping below 50,000 GHz, which is undesirable.

If c is less than 0.333 mol ratio, or is lowered, falling to 35 or lower, which is undesirable; if it exceeds 0.412 mol ratio, εr increases, but the Qf₀ value drops below 50,000 GHz, which is undesirable.

If d is less than 0.333 mol ratio, εr is lowered, falling to 35 or lower, which is undesirable; if it exceeds 0.412 mol ratio, εr increases, but the Qf₀ value drops below 50,000 GHz, which is undesirable.

If e is less than 0.035 mol ratio, εr is increased, but the Qf₀ value drops below 50,000 GHz, which is undesirable; if it exceeds 0.167 mol ratio, εr is lowered, falling to 35 or lower, which is undesirable.

If f exceeds 0.101 mol ratio, If becomes quite large, becoming 10 ppm/° C. or more, which is undesirable.

EXAMPLES Example 1

As starting raw-material powders, high purity powder of Al₂O₃, Ga₂O₃, TiO₂, SrCO₃, La₂O₃ and Pr₆O₁₁ were blended as shown in Table 1, calcined for two hours at 1200° C., then pulverized to 1.0 μm then granulated by adding a binder and molded into discs of diameter 12 mm×thickness 25 mm with a molding pressure of 1.5 T/cm². After this, the binder was removed and sintering was performed for four hours at 1500° C. in the atmosphere. The sintered body obtained was then cut to a diameter of 10 mm×thickness 4.5 mm to obtain samples. The samples of the Examples which were obtained were evaluated in regard to dielectric performance by the H&C method using a network analyzer. The results are shown in Table 2.

Comparative Example 1

For comparison, powder of high purity identical with that of Example 1 was blended as shown in Table 1, a molding manufactured, and samples manufactured by obtaining a sintered body. The samples of the Comparative Examples which were obtained were evaluated in regard to dielectric performance by the H&C method using a network analyzer. The results are shown in Table 2.

TABLE 1 Composition aAl₂O₃.bGa₂O₃.cTiO₂.dSrO.eLa₂O₃.fPr₂O₃ a b c d e f present invention  1 0.124 0.000 0.375 0.375 0.113 0.013  2 0.114 0.010 0.375 0.375 0.113 0.013  3 0.114 0.011 0.375 0.375 0.063 0.062  4 0.097 0.010 0.394 0.394 0.053 0.052  5 0.132 0.013 0.355 0.355 0.073 0.072  6 0.114 0.011 0.375 0.375 0.125 0.000 comparative example  7 0.067 0.004 0.429 0.429 0.028 0.043  8 0.180 0.009 0.310 0.310 0.172 0.019  9 0.103 0.021 0.375 0.375 0.113 0.013 10  0.150 0.008 0.342 0.342 0.047 0.111 11  0.125 0.000 0.375 0.375 0.125 0.000

TABLE 2 Dielectric characteristic Temperature Relative coefficient permittivity Qf value τf εr (GHz) (ppm/° C.) present invention  1 38.3 54000 −3.3  2 38.0 72000 −3.1  3 38.1 68000 +0.5  4 42.0 52000 +0.8  5 35.5 80000 +0.6  6 38.1 73000 −9.0 comparative example  7 45.0 38000 +2.3  8 31.0 110000  −8.0  9 38.0 29000 −9.5 10  38.2 51000 +13.2 11  38.3 50000 −15.0

INDUSTRIAL APPLICABILITY

According to the present invention, in a La₂O₃.Al₂O₃.SrO.TiO₂ based ceramic composition, by adding specific amounts of Ga₂O₃ and Pr₂O₃, a dielectric ceramic composition for microwave use having relative permittivity εr of 35 to 45 and Qf₀ value of more than 50,000 GHz (at 7 GHz), and dielectric characteristic of τf=0±10 ppm/° C. can be provided; this is a very suitable material for filters for microwave communication, filters for milliwave communication, oscillators, dielectric antennas, and frequency regulating rods etc. 

What is claimed is:
 1. A dielectric ceramic composition for microwave use wherein the compositional formula is expressed by aAl₂O₃.bGa₂O₃.cTiO₂.dSrO.eLa₂O₃.fPr₂O₃ where a, b, C, d, e and f represent the mol ratios and satisfy the following values: a+b+c+d+e+f=1 0.079≦a≦0.167 0<b≦0.017 0.333≦c≦0.412 0.333≦d≦0.412 0.035≦e≦0.167 0≦f≦0.101.
 2. A dielectric ceramic corn position according to claim 1, wherein 0.010≦b≦0.017.
 3. A dielectric composition according to claim 1, wherein 0 <f≦0.101.
 4. A dielectric composition according to claim 3, wherein 0.013≦f≦0.101.
 5. A dielectric composition according to claim 4, wherein said composition has a relative permittivity, εr, of 35 to 45, a Qf₀ value of at least 50,000 GHz at 7 Ghz, and a dielectric characteristic of τf=0±10 ppm/° C. 